Expansion screw for orthodontics

ABSTRACT

Expansion screw for orthodontics, comprising at least one stem ( 1 ) with at least a threaded portion ( 10 ) extending along the longitudinal extension of the stem ( 1 ), at least one receiving body ( 3 ) adapted for receiving said threaded portion ( 10 ) and provided with a complementarily threaded hole allowing said threaded portion ( 10 ) to be screwed therein, guide means ( 2 ) allowing said at least one receiving body ( 3 ) to be moved, actuation means ( 11, 12 ) for actuating said stem ( 1 ). The hole ( 31 ) of said at least one receiving body ( 3 ) has a longitudinal extension substantially corresponding to that of the threaded portion ( 10 ) of said at least one stem ( 1 ). The receiving body ( 3 ) is a technopolymer receiving body and the stem ( 1 ) is embedded in the technopolymer of the receiving body when the expansion screw ( 100 ) is made.

The present invention relates to an expansion screw for orthodontics, inparticular for manufacturing orthodontic appliances comprising platesmade of synthetic resin materials. The invention further concerns a toolfor handling and positioning the orthodontic screw during the formingstep of the plate that receives it.

A bidirectional expansion screw for orthodontics generally comprises acentral stem with counter-rotating threads on the sides with a central“maneuvering” portion of greater diameter, to allow its rotation bymeans of a tool plug insertable into the recesses or holes provided onits surface. The stem of the screw is associated with two guidesconstituted by cylindrical parallel rods interconnected by metal blockswhich have longitudinal holes in which the same rods are made to pass,so as to form a guide assembly for handling the blocks with thecorresponding separate portions of the orthodontic plate. In each of theblocks connecting the guide rods is provided a threaded hole intended toreceive a corresponding side of the central stem.

Expansion screws of this type are disclosed in IT1163244, U.S. Pat. No.5,472,344, GB641139, as well as in EP868888 and DE20010279. One aim ofthe present invention is to provide a new type of expansion screw havinga structure offering a higher functionality, both during the realizationof the orthodontic plat and in configuration of use.

This result is achieved by providing an expansion screw for orthodonticappliances having the features listed in claim 1. Other features of thepresent invention are the subject of the dependent claims.

The present invention offers the following advantages: the manufacturingprocess is improved; the interaction between the stem and the receivingbodies in which it is screwed is also improved; the expansion screwexhibits a higher resistance to mechanical stresses; the manufacturingand the use of the orthodontic appliance are simplified.

These and other advantages and features of this invention will be bestunderstood by anyone skilled in the art from the following descriptionand with the help of the attached drawings given as a practicalexemplification of the invention, but not to be considered in alimitative sense, wherein:

FIG. 1 is a perspective view with sectioned parts of a possibleembodiment of an orthodontic screw in accordance with the presentinvention;

FIGS. 2 and 3 are plan views with sectioned parts of the example shownin FIG. 1, represented in two different positions, respectively, theminimum and maximum expansion position;

FIG. 4 is an exploded perspective view of the example shown in theprevious drawings, with a tool for its handling that can be used, inparticular, during the positioning of the screw for the association tothe resin plates which form the orthodontic appliance;

FIG. 5 shows the example of FIG. 4 in the assembled configuration;

FIG. 6 is a schematic plan view representing an orthodontic plateprovided with an orthodontic screw made according to the presentinvention, the orthodontic screw being represented in a plan view withsectioned parts;

FIG. 7 shows cross-sectional views of possible embodiments of the guideelements of an orthodontic screw according to the invention;

FIGS. 8 and 9 are plan views showing other embodiments of a screwaccording to the present invention, respectively, in the form of amono-directional expansion screw (FIG. 8) and three-directionalexpansion screw (FIG. 9); the drawings show plan views with sectionedand with the screws in a configuration of maximum expansion;

FIG. 10 is a perspective view of another example of orthodontic screwaccording to the present invention, shown in the assembled configurationtogether with the tool for its handling, and in which indicators of thedirection of activation of the screw are provided;

FIG. 11 is a graph that illustrates the difference between thecompression response provided by means of an orthodontic screw madeaccording to the present invention and by means of a conventionalorthodontic screw;

FIG. 12 schematically represents an apparatus designed to obtain thegraph of FIG. 11;

FIG. 13 represents a possible embodiment of the screw (1);

FIGS. 14 and 15 show another embodiment of an orthodontic screwmanufactured in accordance with the present invention;

FIGS. 16A-16F schematically show a process for forming the orthodonticscrew (100) according to the present invention.

With reference to the attached drawings, an expansion screw (100) fororthodontic resin appliances comprising resin plates according to thepresent invention comprises at least one stem (1) with at least athreaded stem portion (10) extending along the stem (1). The screw (100)further comprises at least one receiving body (3) for the threaded stemportion (10) of the stem (1), provided with a complementarily threadedhole for receiving said portion (10) so as to allow the screwingthereof, guide means (2) for guiding said at least one receiving body(3) and driving means (11, 12) for making the stem (1) to rotate aboutits own axis. With reference to FIGS. 1-7, the screw can be of thebidirectional type, i.e. of the type comprising two differently threadedopposite stem portions (10) (for example anti-clockwise threading to theleft and clockwise threading to the right) to determine, in a known way,the contemporary spacing of the two receiving bodies (3) with respect tothe central driving portion (11) of the screw to cause the correspondingdistancing of the portions (7) of an orthodontic resin base plate; inFIG. 6 the arrow (F) shows the possible movements of the plate portions(7) and (D7) denotes the space between the same portions of the baseplate.

The orthodontic appliance shown in FIG. 6 is formed by the screw (100)and the base plate including said portions (7). The base plate has sideedges intended to contact the lingual side of the teeth. The screw (100)is incorporated into the resin of the base plate according to methodsknown to those skilled in the art.

The threads of the threaded stem portions (10) of the screw can have atrapezoidal profile, as shown by way of example in FIG. 13, thusoffering a greater resistant cross section, or they can have any othersuitable profile, being entirely eliminated the construction constraintsrelated to the need of threading the receiving body. In fact, thethreads (10) are copied perfectly inside the receiving body (3) when thelatter is formed, as further described in the following.

The central driving portion (11) is substantially cylindrical; inparticular, the central portion (11) extends along the stem (1) for afirst value (H11) and projects radially from the central driving portionof the stem (1) for a second value (D11). The holes (12) provided by theportion (11) are used to obtain the rotation of the stem (1) for theoperation of the orthodontic screw (100) by means of a tool that can beinserted into said holes.

According to the present invention, the hole (31) of the receiving body(3) has a longitudinal extension substantially corresponding to that ofthe threaded portion (10) of the stem (1). In practice, the body (3) ismade of a plastic material, in particular technopolymer that, in phaseof realization of the screw (100), is associated to the other parts ofthe orthodontic screw (100). When the orthodontic screw (100) ismanufactured, the stem (1) and the guide means (2) are embedded in thetechnopolymer that constitutes the receiving body (3). In this way, thethreaded portions of the stem (1) are completely covered by thetechnopolymer of the receiving body, thus offering a double advantage:the threads (30) of the body (3) are exactly complementary to thethreads (10) of the stem (1) and the threads (10) do not remainuncovered and, therefore, are not affected by the subsequentincorporation into the resin of the base plate during the formation ofthe orthodontic appliance. In fact, the next phase of the processprovides for the embedding of the orthodontic screw (100) in the resinof the base plate; in this way, the friction (due to the engagementbetween stem 1 and body 3) will be independent from the characteristicsof the resin chosen for making the base plate and will not depend on theprocess chosen for manufacturing the latter. Suitable technopolymers canbe, for example, polyoxymethylene (POM), polyamide (PA), polysulfone(PPSU) or talc filled polypropylene.

FIGS. 16A-16F schematically show a process for forming the orthodonticscrew (100): a mould (M) is provided, having a moulding cavity (MC), asshown in FIG. 16A; then, the stem (1) is positioned in the mouldingcavity (MC) as shown in FIG. 16B; in a next step, the guides (2) arepositioned at the sides of the stem (1) as shown in FIG. 16C; in a nextstep, the mould is closed, as shown in FIGS. 16D and 16E and thetechnopolymer is injected into the cavity (MC), for example by means ofa screw-type plunger (P) to force the molten plastic material, i.e. thetechnopolymer, into the mould cavity (the plunger P is better visible inFIG. 16E); finally, as shown in FIG. 16E, the mould (M) is open and thethus formed screw (100) can be extracted from the mould.

In addition, the guide means (2) advantageously comprise a substantiallyflat body with a cross-section having a first dimension (H2)substantially smaller than a second dimension (L2). FIG. 7 shows somepossible embodiments of the guides (2). The flat shape of the guides (2)allows for improved force transmission; in practice, since these guidesare substantially flat, the transmission of forces to the teeth of thepatient is more gradual due to the higher flexibility thus acquired bythe device that ensures a corresponding progressive release of forces.By suitably sizing the guides (2) it is possible to adjust theflexibility of the orthodontic device, i.e. the gradual release of theforces. This leads to advantages in the step of positioning theappliance in the oral cavity after a possible interruption of thetherapy.

FIG. 11 is a graph showing the results of tests concerning the stiffnessresponse to compression of a screw with a plastic body manufactured inaccordance with the present invention in comparison with a standardsteel screw manufactured by Leone Spa, model No. A0805, identified with(K) in the graph.

The tests performed by the applicant allowed an instrumental check ofthe magnitude and the releasing conditions of a force by the expansionscrew (100) described above compared to a standard screw (K). Inparticular it has been verified that the greater flexibility of thescrew (100) with plastic bodies and rectangular cross section guides(AISI 301/3021, thickness 0.6 mm, screw thread M2) instead of circularcross section allows insertion in a same orthodontic model with agreater number of initial activations as compared to the conventionalmore rigid expansion screw entirely made of steel and circular crosssection guides (that in the tests were of a diameter of 1.5 mm, screwthread M22). For executing the test, removable plates were made adaptedto fit to the same orthodontic model; the plates were identical to eachother, except, for the expansion screw positioned inside them. Each ofthe resin plates was divided into two halves in turn locked to twoopposite supports, one clamped by a lower clamp (LJ) and the otherclamped by an upper clamp (UJ) of a testing apparatus (AP) made by thesame applicant. The forces were sensed by load cells.

The graph in FIG. 11 shows the stiffness curves of the two devicessubjected to the test, starting from a closed screw configuration. Fromthe curves it can be seen that the orthodontic screw (100) in accordancewith the invention is characterized by a lower stiffness than aconventional expander (K). In other words, for an equal number ofactivations, the expander of the present invention performs a lowercompression force and it is possible to fit it in the model with ahigher number of activations, i.e. a higher number of turns of thescrew, compared to the conventional screw-operated expander.

Referring to the detected values, it is noted that with two activations,corresponding to an expansion of 0.4 mm, the screw of the conventionaltype (K) determines a load comprised between 10 and 20 N, i.e. about15N, while the screw according to the invention (100) determines a loadcomprised between 0 and 10 N, i.e. about 7N; with four activations,corresponding to an expansion of 0.8 mm, the screw of the conventionaltype (K) determines a load higher than 50 N, i.e. about 51N, while thescrew according to the invention (100) determines a load comprisedbetween 30 and 40 N, i.e. about 36N.

Furthermore, since the body (3) is made of a technopolymer, instead of ametal material, it can be colored and more visible.

The guide means (2) are constituted by a body which extends towards saiddriving portion (11) copying its profile. In particular, since saiddriving portion (11) is cylindrical, said guide means (2) are providedwith an appendix (20), which interacts with the driving portion (11),provided with a cavity with rectangular profile extending along thelongitudinal direction of the stem (1) and radially to such direction.The longitudinal and the radial length of said cavity correspondrespectively to said first (H11) and said second value (D11).

With reference to the drawings (in particular FIGS. 1-7), the guidemeans (2) comprise two lateral elements arranged at the two sides of thestem (1) and inserted in the body for receiving (3) through two holes(32) arranged the sides of the first threaded hole (31), said lateralelements (2) being both provided with said appendix (20). The guidemeans (2) contribute to the correct positioning and to the correcthandling of the orthodontic screw (100) not only because theirrespective lateral elements are inserted in the holes (32) of the body(3), but also for the appendixes (20) that are arranged at the sides ofthe driving portion (11).

As shown in FIGS. 4 and 5, a positioning element or tab (6) is provided,formed by two parts or semi-tabs (60, 61) that can be used to supportthe orthodontic screw (100) during the formation of the orthodonticplate and to protect the activation holes (12) that, in this way, willnot be filled by the resin; the tab (6) is provided with at least oneappendix (62) stably insertable in a cavity (12) of said screw (100). Inparticular, the appendix (62) is constituted by a cylindrical body (inthis example, one for each portion of the tab 6) insertable into one ofthe holes (12) of the driving portion (11); in this way, during theformation of plate the elements destined to form the orthodonticappliance are firmly kept united to each other, and the resin isprevented from penetrating into the holes (12).

The two parts (60, 61) of the tab (6) are provided with means allowingtheir stable but reversible coupling. According to the example shown inthe drawings, the upper part (60) is provided, in its lower part, withtwo recesses (66) symmetrically arranged above two corresponding teeth(65). Correspondingly, the lower portion (61), in its upper part, isprovided with two flexible appendices (63) which are superiorly shapedcomplementarily with respect to the recesses (66), and that form twoinner recesses (64) shaped complementarily with respect to the teeth(65) of the upper portion (60). Between the two teeth (65) and the twoappendixes (63) there are arranged the appendixes (62) which areintended to be introduced into the holes (12) of the driving portion(11). In this way, once introduced the appendix (62) of one of the twoportions (60, 61) in one of the holes (12), it is possible to “close”the tab (6) approaching the other portion (61, 60) so as to join thesame portions by distancing the resilient appendages (63) and insertingthem into the recesses (66). This allows a convenient handling of theorthodontic screw (100) retained and supported by the tab (6) and aneasy release of the same.

As represented by way of example in FIGS. 8 and 9, the present inventioncan also be applied to the mono-directional and three-directionalscrews, not only to bidirectional screws such as that describedpreviously, as well as in other screws not shown such as, for example,the so-called “fan-like” orthodontic screws.

In particular, the example shown in FIG. 8 relates to an unidirectionalorthodontic screw, marked with (100), wherein the guide element (2) hasa connecting portion (23) on the side opposite to that from whichemerges the threaded stem portion (10); in practice, the portion (23) ofthe guide element (2) is integral with the corresponding body portion(3) disposed on the right in the drawing, while the part of the guideelement (2) arranged to the left in the drawing is allowed to sliderelative to the body (3) inside the hole (32), as provided for thebidirectional screw previously described. In the case of unidirectionalorthodontic screw, the threaded stem portion (10) will be engaged onlyon one side (the left side in the drawing) with the corresponding hole(31). The screw (100) represented in FIG. 9 is of the three-directionaltype, with three stems (1) operable in an independent manner, each ofwhich has a respective threaded stem portion (10) passing through acorresponding receiving body (3) and a driving portion (2). Similarly,the principle of the present invention can be applied to so-called“fan-like” orthodontic screws having two hinged arms that can beconnected to the threaded stem portion of a screw also provided with adriving portion. An orthodontic screw of this type is disclosed inIT-0001278739 to which reference can be made for further details.

The screws (100) are provided with the indicator elements (4) that canbe used, as usual, to provide the activation direction of the screw, orto indicate the direction of rotation to be used to “open” the screw,that is to lengthen it. In the example shown in FIG. 10, the indicatorelements (4) is associated with an additional indicator (40) which hasthe shape of an arrow and is provided with two teeth (44) that can beinserted in corresponding seats (34) presented by the body (3).

The additional indicator (40), which can be realized in a differentcolor, is much more visible than the conventional indicator (4); inparticular, when the plate is in the oral cavity, the additionalindicator shows in a very evident way the correct direction for theactivation of the screw.

According to the example shown in FIGS. 14 and 15, the upper semi-tab(60) has an appendix (600) on its upper side (the side opposite to thatof association with the screw). Said appendix (600) is of triangularshape and, on its rear side, has a depression (601) that is alsotriangular in shape and has dimensions corresponding to those of theindicators (4) previously mentioned. The appendix (600) can be easilydetached and fitted on an indicator (4) before being embedded in thetechnopolymer. The depression (601) on the back of the appendix (600)facilitates this operation. In this way, it is provided a further andmost noticeable indication of the direction of activation of theexpansion screw, in particular when the tab (6), and thus the appendix(600), is made of a material having a color contrasting with that of thetechnopolymer of said receiving body.

It is understood that, more in general, the depression (601) has theshape and dimensions corresponding to those of the indicators (4) whichmay also be non-triangular although it is believed that the triangularshape is particularly suitable to indicate the direction of activationof the screw. The materials used to make the present orthodonticappliance are biocompatible. On the sides of the tab (6) can beimprinted the name of the manufacturer or any other sign (M).

The invention is not limited to the examples described and illustratedabove, but it may vary as regards the nature and arrangement of itsparts, without departing from the inventive teaching here disclosed andclaimed.

The invention claimed is:
 1. An expansion screw for orthodontics, theexpansion screw comprising: at least one stem with at least a threadedportion extending along a longitudinal extension of said at least onestem; at least one receiving body adapted for receiving said threadedportion and provided with a complementarily threaded hole allowing saidthreaded portion to be screwed therein; a guide means allowing said atleast one receiving body to be moved; an actuation means for actuatingsaid at least one stem, said hole of said at least one receiving bodyhaving a longitudinal extension substantially corresponding to said atleast one stem, said receiving body being a technopolymer receiving bodyand said at least one stem being embedded in technopolymer of saidreceiving body when said expansion screw is made, said technopolymerreceiving body comprising said technopolymer, wherein said guide meanscomprises a substantially flat body, said substantially flat body havinga cross section with a first dimension substantially smaller than asecond dimension.
 2. An expansion screw according to claim 1, whereinsaid at least one stem is provided with a driving portion, said guidemeans comprising a body that extends towards said driving portion, saidbody comprising a body profile, said driving portion comprising adriving portion profile, said driving portion profile corresponding tosaid body profile.
 3. An expansion screw according to claim 2, whereinsaid driving portion is cylindrical, extending along said at least onestem for a first value and protruding, with respect to said at least onestem, for a second value, and said guide means comprising an appendix,adapted to interact with said driving portion, provided with a cavityhaving a rectangular profile and extending along a longitudinaldirection of said stem and radially with respect to said longitudinaldirection, said rectangular profile having dimensions correspondingrespectively to said first value and said second value.
 4. An expansionscrew according to claim 3, wherein said guide means comprises twolateral elements disposed on either side of said at least one stem andinserted into said receiving body in two holes arranged at sides of saidthreaded hole, said lateral elements being both provided with saidappendix.
 5. An expansion screw according to claim 1, furthercomprising: a positioning element or tab formed by two parts coupledtogether to support said screw during formation of an orthodonticapparatus or plate, said tab being provided with at least one protrudingappendix adapted to be stably inserted in a cavity of said screw.
 6. Anexpansion screw according to claim 5, wherein said at least one stem isprovided with a driving portion having at least one actuating seat, saidseat being a hole and said appendix being a cylindrical body adapted tobe inserted in said hole.
 7. An expansion screw according to claim 1,wherein said screw comprises a single stem defining a mono-directionalscrew.
 8. An expansion screw according to claim 1, wherein said screwcomprises three stems defining a tri-directional screw.
 9. An expansionscrew according to claim 1, further comprising: one or more pointersadapted to indicate an activation direction.
 10. An expansion screwaccording to claim 9, wherein at least one of said one or more pointersis removably associated with a positioning element or tab.
 11. Anexpansion screw according to claim 10, wherein said at least one of saidone or more pointers is removably associated with a part of saidpositioning element or tab.
 12. An expansion screw according to claim 1,wherein said at least one receiving body is embedded into a resin baseplate of an orthodontic appliance, said resin base plate comprising twoparts connected with each other by said expansion screw.
 13. Anexpansion screw for orthodontics, the expansion screw comprising: a stemcomprising a threaded portion extending along a stem longitudinalextension of said at least one stem; a receiving body comprising athreaded hole, the threaded hole receiving said threaded portion; aguide means for allowing said receiving body to move, said guide meanscomprising a planar guide body; an actuation means for actuating saidstem, said hole of said receiving body having a receiving bodylongitudinal extension, wherein a length of said receiving bodylongitudinal extension corresponds to a length of said threaded portionof said stem, said receiving body comprising a receiving body portion,said receiving body portion comprising a threaded surface defining oneor more threads of said receiving body and said receiving body portioncomprising a receiving body planar surface defining at least a portionof an opening for receiving at least a portion of said planar guidebody.
 14. An expansion screw according to claim 13, wherein said planarguide body comprises a first appendix on one side of said actuationmeans and a second appendix on another side of said actuation means,said first appendix being adjacent to a first portion of said actuationmeans, said second appendix being adjacent to a second portion of saidactuation means.
 15. An expansion screw according to claim 14, whereinsaid first appendix comprises a first appendix first projection and afirst appendix second projection, said first appendix first projectionand said second appendix second projection being located adjacent tosaid first portion of said actuation means, said second appendixcomprising a second appendix first projection and a second appendixsecond projection, said second appendix first projection and said secondappendix second projection being located adjacent to said second portionof said actuation means, said first appendix first projection facing ina direction of said second appendix first projection, said firstappendix second projection facing in a direction of said second appendixsecond projection.
 16. An expansion screw according to claim 15, whereinsaid first appendix first projection is located at an axially spacedlocation from said first appendix second projection with respect to alongitudinal axis of said planar guide body, said second appendix firstprojection being located at an axially spaced location from said secondappendix second projection.